title: Biodegradation of the allelopathic chemical m-tyrosine by Bacillus aquimaris SSC5 involves the homogentisate central pathway.
abstract: m-Tyrosine is an amino acid analogue, exuded from the roots of fescue grasses, which acts as a potent allelopathic and a broad spectrum herbicidal chemical. Although the production and toxic effects of m-tyrosine are known, its microbial degradation has not been documented yet. A soil microcosm study showed efficient degradation of m-tyrosine by the inhabitant microorganisms. A bacterial strain designated SSC5, that was able to utilize m-tyrosine as the sole source of carbon, nitrogen, and energy, was isolated from the soil microcosm and was characterized as Bacillus aquimaris. Analytical methods such as HPLC, GC-MS, and (1)H-NMR performed on the resting cell samples identified the formation of 3-hydroxyphenylpyruvate (3-OH-PPA), 3-hydroxyphenylacetate (3-OH-PhAc), and homogentisate (HMG) as major intermediates in the m-tyrosine degradation pathway. Enzymatic assays carried out on cell-free lysates of m-tyrosine-induced cells confirmed transamination reaction as the first step of m-tyrosine degradation. The intermediate 3-OH-PhAc thus obtained was further funneled into the HMG central pathway as revealed by a hydroxylase enzyme assay. Subsequent degradation of HMG occurred by ring cleavage catalyzed by the enzyme homogentisate 1, 2-dioxygenase. This study has significant implications in terms of understanding the environmental fate of m-tyrosine as well as regulation of its phytotoxic effect by soil microorganisms.
authors.affiliation: Institute of Microbial Technology, Council of Scientific and Industrial Research (CSIR), Chandigarh, India.
authors.forename: Fazlurrahman
authors.initials: F
authors.lastname: Khan
authors.forename: Munesh
authors.initials: M
authors.lastname: Kumari
authors.forename: Swaranjit Singh
authors.initials: SS
authors.lastname: Cameotra
mesh_terms: D064089:Allelopathy; D001407:Bacillus / Q000201:enzymology / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D055162:Biocatalysis; D050560:Homogentisate 1,2-Dioxygenase / Q000378:metabolism; D006713:Homogentisic Acid / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D012988:Soil Microbiology; D014443:Tyrosine / Q000378:metabolism*; D014444:Tyrosine Transaminase / Q000378:metabolism
chemical_list: C071365:3-hydroxyphenylacetate 6-hydroxylase; D014443:Tyrosine; C015566:3-tyrosine; D006899:Mixed Function Oxygenases; D050560:Homogentisate 1,2-Dioxygenase; D014444:Tyrosine Transaminase; D006713:Homogentisic Acid